Alright. I'm listening. How does Link get ahold of Sheik in the first place, and avoid getting sliced by a million dagger slashes while he's at it?
Well the most obvious solution is to not actually rush into Sheik, and as the match starts, always bring out a bomb, it sets up for Sheik to dodge it when it's thrown and that makes Sheik predictable at that point; if she jumps, Link can U-Air or U-Tilt. If she tries an attack, Link can grab. If she rolls into Link, Spin Attack.
If you want to get her off the stage, the best solution is to use basically any of Link's attacks, or even the Jab > Jab 2 > Spin Attack combo, which does actually work on Sheik, like so many others. Link can avoid Sheik's needles just by not being near them or, like you can reasonably do without punishment, let Link use Hylian Shield, which defeats...all...projectiles. You got rid of Sheik's needle usage on ground until you attack.
But what happens if you get hit by them? Run or perform a counter attack.
What if she starts grabbing you? DI toward her or downward depending on attack, except U-Air, which you should SDI behind or under Sheik.
What if she starts her string of attacks? Wait. There will be an opportunity for you to retaliate; best option is to DI upward if she performs multiple F-Tilts, so that she can't grab you and it gives you enough time to bring out a retaliating N-Air.
If you want to avoid Sheik's attacks when you get up back from the ledge, use the F-Air/N-Air/Z-Air/Bomb get up. F-Air is good for distancing and may land you a potential 24% damage hit, N-Air gets her away, Z-Air does the same, but with more range and bomb literally sets up for anything you can get out of it.
What if Sheik goes for a B-Air or F-Air on the ledge to stage spike? Don't worry, a simple calculated read with U-Air will get her away, and if not that, jumping up will avoid a stage spike altogether.
If you also want to avoid a 0-to-Death, here's an easy method; just...DI...vertically. Either way, up or down, you're going to make her miss some attacks; the player would have to read your movements to try to get to you. And hey, if you want to kill Sheik off stage quick, just go brave it out with F-Air.
But of course, the main people who will refute this will probably be people who've not spent even a hundredth of a time on Link that I have.